This invention relates to a fuel injection system for a mixture-compressing spark ignition internal-combustion engine, and particularly to a fuel-metering system to provide exact metering of the quantity of fuel to be injected into each cylinder of the internal-combustion engine.
On the basis of DE-PS No. 31 43 492, a mixture-compressing spark ignition internal-combustion engine for motor vehicles is known having a main combustion chamber and a precombustion chamber where a spark plug and a precombustion chamber injection nozzle are arranged. The precombustion chamber injection nozzle can be switched on and off as a function of the load, and the quantity of its injection can be influenced as a function of the load. In this case, fuel is supplied to the precombustion chamber injection nozzle via a typical fuel-metering device. The shifting of the control piston in this case takes place only by means of the fuel acting upon one front side of the control piston in cooperation with the pressure spring. In the case of this fuel-metering device, the fuel has no other function than that of acting upon one front side of the control piston. The control piston has a sloped control edge by means of which the fuel supply is controlled via control openings to several injection nozzles. For this purpose an exact positioning of all control openings in axial direction is required. The control piston is driven by the camshaft. For this purpose, the control piston has a blocking journal on the end side provided with a blocking slot. The blocking journal is guided in a pocket bore in a control journal of the camshaft. Here an additional sealing at the control piston is required, and this control piston must be arranged so that it is in alignment with the camshaft.
One object of the present invention is to provide a fuel injection system for a mixture-compressing spark ignition internal-combustion engine having a fuel metering device that is simple to manufacture and easy to assemble, exhibits extreme operational reliability, and ensures an exact metering of fuel.
An exact metering of the quantity of fuel to be injected separately into each cylinder of the internal-combustion engine is made possible by means of the fuel injection system according to the present invention. In order to achieve an identical injected quantity in the case of all fuel metering devices, the prestressing of the pressure springs is affected by an adjustment of the motor housing parts and the parts of the control piston housing with respect to one another. Repercussions on the fuel quantity by characteristic-line tolerances of the pressure springs are balanced by the adjusting screws. A constant fuel-air mixture ratio can be achieved by correct coordination of the air volume meter, the pressure regulator in the final return line, the pressure spring, and the circular-arc-shaped area segment. The circular-arc-shaped area segments permit a linear control of the fuel quantity to be injected via an axial shifting of the control pistons. The tangential start of the surface segments permits the linear start of the fuel quantity to be injected starting from zero. The fuel cools not only the electric motor but also the control pistons resulting in the avoidance of the formation of steam bubbles at the control openings. The hydraulic coupling of the fuel-metering devices and the arrangement of an electric motor in each fuel metering device permits the arrangement of said fuel-metering device in each fitting position. The electric motor must not be aligned exactly with the control piston, and sealings at the side of the drive are not necessary. The fuel injection system of the present invention can be built from identical structural parts for all internal-combustion engines - irrespective of the number of cylinders - due to the provision of a fuel-metering device for each cylinder of the internal-combustion engine. If, for example, two recesses are provided that are arranged at the circumference of the control piston so that they are evenly distributed, the pressure force of the control piston on the control cylinder is very little so that electric motors with only a low driving capacity are required.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purpose of illustration only, preferred embodiments in accordance with the present invention.